1. Field of the Invention
A method of preventing, or decreasing the severity of symptoms associated with a respiratory viral infection in a mammal is provided. Also provided is a method of gene therapy capable of causing expression of IFNxcex3 in respiratory cells for prevention of viral infection.
2. Description of Related Art
Respiratory viruses such as respiratory syncytial virus (RSV), the parainfluenza viruses (PIV), and the influe nza viruses cause severe lower respiratory tract diseases in infants and children throughout the world. It is also an important cause of disease in adults and is responsible for a significant amount of excess morbidity and mortality in the elderly. It also can be devastating in immunosuppressed populations (Murray et al., 1997; Pullen et al. 1982; Hall et al. 1984).
Experimental live attenuated vaccines for each of these viruses are being developed for intranasal administration in the first weeks or months of life, but none are currently FDA approved. A variety of RSV, PIV-3, and influenza virus vaccine strains have been developed by classical biological methods, evaluated extensively in preclinical and clinical studies, and shown to be attenuated and genetically stable. However, a major remaining obstacle to successful immunization of infants against respiratory virus associated disease may be the relatively poor immune response of very young infants to primary virus infection. (Crowe J. E. Jr Vaccine 1998 Aug.-Sep.;16(14-15):1423-32 Immune responses of infants to infection with respiratory viruses and live attenuated respiratory virus candidate vaccines.)
Moreover, even if one or more vaccines are approved, they may not be suitable for some populations vulnerable to RSV (e.g. very young infants and the immunosuppressed). Ribavirin and immunoglobulin preparations with high titers of RSV-specific neutralizing antibodies are currently approved for use to treat and prevent RSV infection. However, neither of these methods are cost-effective or simple to administer. New agents are needed to reduce the impact of RSV. (Wyde P. R. Antiviral Res 1998 Aug.;39(2):63-79 Respiratory syncytial virus (RSV) disease and prospects for its control.)
Data obtained from the National Respiratory and Enteric Virus Surveillance System demonstrates the seasonal pattern of RSV infection, with peak rates of 30-40% occurring at the beginning of each year (Murray et al., 1997; Pullen et al. 1982; Hall et al., 1984). RSV infection is commonly associated with interstitial lung diseases, such as bronchiolitis and asthma. It is a major risk factor for a number of other disease conditions, such as immunodeficiency, cardiac arrhythmia, congenital heart disease, and unusual atrial tachycardia (Sly, et al., 1989; Robinson et al. 1997;
Armstrong et al. 1993; Fixler, 1996; Lemen, 1995; Persson, 1997; Shelhamer et al. 1995).
Emerging evidence points to RSV as a significant pathogen in adults and the elderly (Murray et al., 1997). In the USA alone, RSV causes about 4500 deaths per year, about 95,000 hospitalizations, and an estimated four million cases of respiratory tract infections annually (McIntosh et al., 1990; Hall, et al. 1991). RSV is also a major public health concern globally with an estimated five million deaths annually due to RSV infections (Warren, 1986; Walsh, 1988).
Although the severity of the disease decreases with repeated infection, previous RSV infection renders no or limited immunity to subsequent RSV infection (Hal, 1991).
Despite the above serious implications of RSV infection, the progress in the knowledge of the viral genes and gene products (Collins, 1991; Collins et al., 1996; Barik, 1992), an effective vaccine, or treatment against RSV, is yet to be developed.
Additionally, previous attempts to develop a vaccine using formalin inactivated RSV not only failed but exacerbated the disease when subsequent RSV infection occurred (Chanock, et al. 1992; Hall, 1994). The development of an attenuated, immunogenic and genetically stable live RSV vaccine has not been successful. An effective vaccine or treatment for RSV would be highly desirable.
Additionally, human nasal, airway, and lung epithelial cells constitute a major target for respiratory infections. Viral infection alters the expression of genes encoding a number of cytokines, chemokines and inflammatory mediators (Sabauste, et al. 1995; Choi, et al. 1992; Becker et al. 1993). However, the molecular mechanism underlying RSV infection and receptors for RSV remain to be elucidated.
The molecular pathology of RSV infection-induced inflammation, which is poorly understood, has been investigated. The alteration of gene expression for various cytokines, chemokines, and inflammatory mediators was examined using RT-PCR and ELISA assays following RSV infection of HEp-2 and BEAS-2B cells. The expression of the inflammatory cytokines IL-6, IL-8, IL-10 and IL-1xcex2 increased with the time of exposure to RSV. Both cell lines constitutively expressed IL-13 MRNA.
The expression of the chemokine, RANTES, and the broncho-constrictor, endothelin-1, were also increased after viral infection in both cell lines. The expression of other inflammatory mediators, such as inducible nitric oxide synthase (iNOS) and mucin-1 (MUC1) encoding episialin, a mucin like polypeptide, also increased after viral infection. Only the BEAS-2B cell line expressed TNF-xcex1 following viral infection. These results demonstrate that RSV infection triggers the production in these epithelial cells of several of the pro-inflammatory cytokines and mediators, responsible for the airway inflammation in both allergic and non-allergic individuals.
The secretion of cytokines by airway epithelial cells can either initiate local inflammatory responses or amplify an inflammatory event that was previously initiated by activated macrophages, eosinophils, mast cells or lymphocytes (Shelhamer et al., 1995; Holtzman, et al. 1991; Churchill, et al. 1989; Marini, et al. 1992; Churchill, et al. 1992; Kwon, et al. 1994; Sousa, et al. 1994; Cromwell, et al. 1992; Jin, et al. 1997). The epithelial cell-mediated inflammation by involve a number of cytokines and chemokines including IL-1xcex2, IL-6, IL-8, IL-11, IFN-xcex3, TNF-xcex1, GM-CSF, GRO-xcex1, PLA-2, C3, inducible nitric oxide synthase (iNOS), MCP-1, endothelin-1 (ET-1), mucin, elastase-specific inhibitors, and secretory leukocyte proteinase inhibitor.
Available evidence suggests that the primary target of respiratory viruses are epithelial cells. Once infected, epithelial cells respond to the virus by increasing the production of a number of cytokines, which contribute to airway inflammation (Sabauste, et al. 1995; Choi, et al. 1992; Becker et al. 1993; Merolla, et al. 1995; Noah, et al. 1993; Garofalo et al. 1996). The rhinovirus infection of a transformed HBE cell line, BEAS-2B, caused the release of the granulocyte macrophage colony stimulating factor (GM-CSF), IL-6, and IL-8 (Sabauste et al. 1995). The influenza virus infection of primary cultures of human bronchial epithelial (HBE) cells induced the expression of IL-8 (Choi, et al. 1992). Also, in response to RSV infection, nasal epithelial cells and BEAS-2B cells generated IL-8 (Becker et al., 1993; Merolla et al., 1995; Noah, et al., 1993; Garofalo et al. 1996). Although the cytokine-mediated inflammatory basis of respiratory infections has been investigated, the molecular mechanisms underlying such infections remain poorly understood.
Studies in children suggest that RSV infection induce a T helper type 2-like response (Roman, et al. 1997). Also, formalin inactivated RSV induces a Th2-like response and IgE antibody production in mice (Connors, et al. 1992; Connors, et al. 1994; Graham, et al. 1993). Th2-like cells are mediated via cytokines such as IL-4, IL-5, IL-10, and IL-13 (Mosmann, et al. 1989) which are either important for IgE production or are involved in the recruitment and activation of inflammatory cells. IL-4 and IFN-xcex3 reciprocally regulate IgE production, and RSV infection can augment IgE mediated inflammation in individuals genetically predisposed to develop atopic disease (Roman, et al. 1997). RSV infection is also associated with recurrent episodes of bronchial obstruction and exacerbation of established asthma in some children with atopic genetic predisposition (Mok, et al. 1984; Weiss, et al. 1985; Sly, et al. 1989). Acute viral respiratory tract infections also enhance sensitization to inhalant allergens in mice (Schwarze, et al. 1997). Although the mechanism underlying this synergy is not fully characterized, it may be mediated via the T cell response.
A number of investigators have examined the effect of IFNxcex3 on epithelial cells (Boehm et al. 1997). Exposure to IFN-xcex3 to 84% epithelial cells resulted in increased surface expression of MHC class I molecules, xcex2-2 integrins and ICAM-1 (Colgan, et al. 1994). Pretreatment of a KB human epithelial cell with IFN-xcex3, augmented the expression of ICAM-1 (Dao, et al., 1995). In an effort to define the role of IFNxcex3 on T84 epithelial cells, Adams et al., 1993 showed that only the monolayers basolateral surface was IFNxcex3 responsive, and the microvillus surface was not. The effects of IFN-xcex3 were recepter-ligand mediated and IFN-xcex3 induced changes in epithelia permeability. Moreover, IFN-xcex3 treatment of the A594 lung epithelial cells, blocked the attachment of Pneumocystis carinii, to the cells via reduced expression of xcex22-integrins (Pottratz et al. 1997). IFNxcex3 was also shown to decrease the susceptibility of epithelial cells to infection by rhinovirus, although rhinovirus infection did not markedly alter the expression of the receptor ICAM-1. Also, IFNFxcex2 markedly inhibited RSV replication in a dose-and time-dependent manner, and IFN-xcex2 did not induce cell membrane damage, cause cell lysis, or inhibit cellular protein synthesis (Garofalo et al. 1996).
It would therefore be useful to develop a vaccine for preventing a respiratory viral infection by the intranasal administration of an IFN-gamma gene which can be given to an infant or other immunosuppressed individual for prophylaxis against respiratory infection, for example. RSV.
According to the present invention, a method of preventing a respiratory infection by administering DNA which encodes IFN is provided. Also provided is a therapy for the prevention of a respiratory infection containing DNA which encodes IFN.